The present invention relates generally to flow meters for use in fuel dispensing environments. More particularly, the invention relates to an inferential flow meter adapted to have enhanced accuracy when pulsations occur in the flow.
Inferential flow meters, e.g., a turbine flow meter, may be used in a variety of applications in fuel dispensing environments. For example, turbine flow meters are often used to meter fuel being dispensed, measure the vapor being returned to the underground storage tank in a stage two vapor recovery fuel dispenser, or measure the vapor or air released to atmosphere from the ullage area of an underground storage tank when a pressure relief valve in a vent stack is opened to relieve pressure.
Turbine flow meters generally comprise a housing having inlet and outlet ports at respective ends thereof. A shaft is located inside the housing along the housing's longitudinal axis. One or more turbine rotors mounted on the shaft rotate when fluid (liquid or gas) flows through the housing via the inlet and outlet ports. A detector is typically mounted to the housing to detect rotation of one or both of the rotors. For example, the detector may be a hall effect device or pickup coil that determines rotation based on changes in a magnetic field. The detector is associated with a “pulser” that produces a series of pulses at a rate which is related to the flow rate of fluid through the meter. As such, the flow rate of the fluid flowing through the housing can be determined.
Various events—such as the operation of submersible turbine pump (STP) motors, the operation of valves in the fuel flow path, or nozzle snaps—can cause substantial flow pulsations. Nozzle snaps, for example, occur when the nozzle is suddenly closed by the customer, or by a valve within the nozzle that automatically closes when the customer's fuel tank is full. These flow pulsations create transients that flow back and forth quickly through the entire hydraulic system for a few seconds. As the pulsations travel through the meter, the instantaneous speed of the turbine rotor(s) varies momentarily in response to the fluid perturbation.
Meters known in the art calculate fluid flow rates based on counting the number of pulses during a programmable time window. The number of pulses is divided by the time window to derive pulses per unit of time. Calculating an average in this manner filters out instantaneous speed variations. As a result, errors in viscosity calculation and flow rate can occur.
Various turbine meters of the prior art are shown and described in U.S. Pat. Nos. 7,028,561, 6,854,342, 6,692,535 and 5,689,071. Each of these patents is incorporated herein by reference in its entirety.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.